This invention relates to compounding mica and certain melt forming resins with discrete, particulate heat sensitive additives, such as chlorinated waxes, that act as coupling agents therefor and includes, in particular, a compounding operation that permits advantageous temperature control and rapid development of desirable physical properties.
U.S. Ser. No. 970,822 and 970,839, each filed Dec. 18, 1978 by Meyer and Newman disclose that certain chlorinated aliphatic compounds can act as coupling agents for mica and certain melt forming resins.
French Pat. No. 2,124,315 discloses a variety of techniques for compounding mica into an organic polymeric matrix and suggests dispersing the mica particles in thermoplastic resin prior to attainment of processing conditions.
A process has now been discovered that provides for compounding of mica and melt forming resin with such heat sensitive additives as chlorinated waxes at times less than a minute, if desired, whereby molding precursors are prepared that may be used in conventional molding operations to yield molded objects of highly desirable physical properties.
The precise conditions under which such compounding is accomplished are quite critical. Chlorinated aliphatic compounds such as heat sensitive chlorinated waxes herein are subject to reduction or even elimination of beneficial effects upon undesired decomposition with heat. Such decomposition is particularly acute during compounding with melt forming resin and mica particles since the mica particles act as heat sinks that are insulated by the resin during compounding and may, under conditions of high shear and mechanical heat generated thereby during intense mixing, cause compounding temperatures in excess of that which causes undesired decomposition, even though cooling is attempted.
On the other hand, low temperatures during such compounding, even if attainable, can lengthen the time required for coupling agents such as chlorinated waxes or other chlorinated aliphatic compounds to exhibit desired effect and consequently cause perhaps less efficient use of equipment or modification of existing equipment so as to extend periods at elevated temperature.
Even still further, however, very high shear can even cause deterioration of melt forming resin to an extent that the filled resins are undesirably brittle even though other properties may be satisfactory. Thus, for example, the high shear used to provide a molten resin in the process of this invention has to be controlled so as to keep the melt index (ASTM D1238) of the compounded resin preferably below about 15.